I have mentioned Tosia before on the blog...It is a starfish in the family Goniasteridae and its genus name is the Latin word for "Inestimable" which alludes, of course, to the animals' incredible natural beauty!

Tosia, as I define it, is found ONLY in Australia, where it is quite abundant and relatively well-known to the people who study marine biology thereabouts. One species in particular, Tosia australis, occurs widely throughout the temperate southern part of Australia.

(Image courtesy of Kate M. Naughton!)

Taxonomists have been noticing T. australis for YEARS and describing a myriad of species. Over the years, some FOURTEEN species have been described-but refinement of species concepts (and removal of unecessarily redundant species) have whittled down the total number to three.

It has led to the identification of what's called the Tosia australis species complex!! That's what happens when you have a lot of closely-related populations that all may or may not be different species.

Something NEW! Brooding Discovered!
So, for an animal that occurs so close to shore, surprisingly little was known about it. In the 90s it was discovered that Tosia australis was a SPECIAL kind of starfish!! It showed an unusual reproductive behavior: BROODING juveniles! That is to say, its offspring live on the adults.
Not too unusual in vertebrates, but VERY unusual in starfish!

Also, Tosia australis has been known since 1840-so it took over 150 years for them to discover that it brooded juveniles!! So, this led to some close observation.

(Image courtesy of Kate M. Naughton!)

So, the investigative talents of Ms. Naughton and Dr. O'Hara were applied towards the question!

Did the difference in larvae mode also translate into further biological differences??

During a museum visit to Melbourne, I was talking shop with Kate and Tim. I was pretty sure that all the morphological variation in the species complex would translate into regional or environmental differentiation VS. Tim who believed that they would split out by larval type.

Larvae in several other species is highly variable but often did not translate into phylogenetic differences..so I figured it would probably do the same here.

And in fact, I was SO confident I was right, that I wagered a gentlemen's bet with Dr. O'Hara that I would be right!

So-I said: "Go get the DNA and prove me wrong!"

And so they did (and had started before I had made the bet!)

Oops! Guess I just lost 10 bucks!
The final analysis following a survey of many specimens from Victoria, Tasmania, and South Australia supported three different species, including something NEW that hadn't been observed before!!!

T. neossia is very similar to the well-known T. australis but, aside from a bunch of external morphological features, one important feature sets them apart....

The difference is in the Larvae (i.e., juvenile starfish)!

One of the fundamental differences here is that of the difference in larvae between Tosia australis and T. neossia!

The new species Tosia neossia had BOTTOM larvae with large yolky eggs (this kind of egg is called lecithotrophic)!!

(Image courtesy of Kate M. Naughton!)

Unlike more "typical" larvae, these tiny guys were negatively buoyant (that is to say, they sink rather then float)!

They are emitted from the mother and crawl along the bottom using little lobes to get around until they fully develop into larval adults. These little BOTTOM larvae (shown here as early stage larvae) can be seen here (courtesy of Kate Naughton!)

(Image courtesy of Kate M. Naughton!)

Here is where the larvae begin to change into what Kate calls the "tripod phase". These utilize a large lobe that helps move the larvae around before it begins to attach someplace on the ground after developing to the right stage....

(Image courtesy of Kate M. Naughton!)

....And finally, here is the settled larvae (oral view-looking up into the mouth). Note the tiny red dots, which will eventually become the eyespots!

This little fellow will develop into what will eventually become

(Image courtesy of Kate M. Naughton!)

....the adult!

This is in direct CONTRAST to Tosia australis which has SWIMMING juveniles that emerge from the aboral surface (via gonopores on the top surface). In contrast to the larval juveniles of T. neossia, T. australis has eggs that are postively buoyant and are covered with small CILIA!! That is, they have little beating hair-like threads that can keep them swimming before they settle out somewhere.

You learn something new every day! Congrats on the discovery. I came across this new species you've described when doing a CAAB search on T.australis to find it's CAAB code. Question is now how does the 'amateur taxonimist' distinguish between these two species. I have many images of these Seastars taken on dives in and around Port Phillip Bay.

The best way to distinguish between Tosia australis and T. neossia is by colour pattern, but unfortunately it's quite hard to describe! As a brief summary, T. neossia is generally smaller and flatter, and the plates on the oral surface are much more heavily granulated, particularly around the mouth. Re: the colour, you'll find that T. neossia can be *deep breath*: red/black, red/brown, cream/black, cream/brown, cream/red, black/brown; usually there are alternating "strips" of colour, although these may be incomplete (sometimes only a couple of plates along the arc between the arms).

T. australis is... well... everything else! Monochromatic orange, purple/pink/brown starbursts, speckled brown and pink, generally quite spectacular and striking. The alternating strips of colour typically aim at the tips of the arms, where as in T. neossia, they usually aim at the arc between the arms (if that makes sense). I gave a colour plate to Reefwatch Victoria and there's one in the Tosia neossia paper (Invertebrate Systematics October 2009) which illustrates the colour patterns far better than I can describe them.

Hope this helps! Feel free to send me any photos at kmnaughton@gmail.com if you're not sure about a specimen and you want a confirmation.

Are both australis and neossia known from Port Phillip Bay? I have a few Tosia I've photographed in the past, all solid orange-red, and I had them as neossia for a while but I wonder if australis is a better option.

About Me

I pursue starfish related adventure around the world with a critical eye and an appreciation for weirdness.
Support has been courtesy of the National Science Foundation but the views and opinions presented herein are mine and do not reflect the opinions of them or any affiliated institutions.
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